1. Field of the Invention
The present invention relates in general to image processing, and more specifically to reduction of block effect in spatially re-sampled image information for block-based image coding including video coding.
2. Description of the Related Art
Up and down sampling, or more generally, re-sampling, of an image signal is a common function performed in image communication systems, including video systems, to facilitate scaling between different spatial resolutions. The Advanced Video Coding (AVC) standard, Part 10 of MPEG4 (Motion Picture Experts Group), otherwise known as H.264, includes advanced compression techniques that were developed to enable transmission of video signals at a wide range of bit rates or to enable improved video quality at a given transmission rate as compared to earlier video coding standards, such as H.263 and MPEG4-Part 2. The newer H.264 standard outperforms video compression techniques of earlier standards in order to support higher quality video at given bit rates and to enable internet-based video and wireless applications and the like. The standard defines the syntax of the encoded video bit stream along with a method of decoding the bit stream.
In many situations, it is desired to increase the resolution of a video stream for display, such as for zooming functions or for increasing resolution of the video information for display on a higher resolution display device. Up sampling is employed to increase the resolution of the video or image. During the up sampling process, zeroes or placeholder values are inserted into the video stream and each pixel is processed through a filter, such as a low pass filter (LPF) or the like. Since most of the compression schemes or coding standards are block-based, such as particular block sizes of pixels (e.g., 16×16, 8×8, 4×4) or particular coding standards (e.g., DCT or the like), when the decoded images or video frames are up sampled to increase the resolution, the block effects may appear or existing block effects may be exaggerated.
Scalable Video Coding (SVC) is an extension of the H.264 which addresses coding schemes for reliable delivery of video to diverse clients over heterogeneous networks using available system resources, particularly in scenarios where the downstream client capabilities, system resources, and network conditions are not known in advance, or dynamically changing over time. SVC provides multiple levels of scalability including temporal scalability, spatial scalability, complexity scalability and quality scalability. SVC achieves scalability by employing the concept of base and enhanced layers, in which an enhanced layer, or upper layer, is scalable from a lower layer, referred to as a base layer. The base layer should be the simplest form in quality, complexity, spatial resolution and temporal resolution. Complexity generally refers to the level of processing required during the coding process. Temporal scalability generally refers to the number of frames per second (fps) of the video stream, such as 7.5 fps, 15 fps, 30 fps, etc. Spatial scalability refers to the resolution of each frame, such as common interface format (CIF) with 352 by 288 pixels per frame, or quarter CIF (QCIF) with 176 by 144 pixels per frame, although other spatial resolutions are contemplated, such as 4CIF, QVGA, VGA, SVGA, D1, HDTV, etc. In the current development of spatial SVC of JVT, up and down sampling are used for inter-layer texture predictions. Existing re-sampling schemes lack performance in terms of coding efficiency and visual quality.
It is desired to improve the visual quality by reducing the block effects when up sampling image information for display or for inter-layer texture predictions.